Need a low cost business class gigabit firewall router or gigabit firewall wireless router

I work for a company that has grown quite a bit in terms of number of network devices and users.  Having said that, it is still a small business with about 15 employees and 20 devices.  The problem is lately some devices have been dropping off the network.  The current network is setup using residential appliances.  The Comcast cable modem is connected to a Netgear WNDR4000 wireless dual band router, which is then connected to a Netgear GS608 8 port switch.  Four offices and the warehouse are fed to this single switch with 5 network cables being connected to the Netgear GS608 switch.  The four offices and the warehouse all have more residential switches to provide network access to the users and devices.   This is my question, can you recommend a specific low cost small business class device that will connect to the cable modem and will provide routing and firewall and maybe even wireless.  Or at least a firewall router plus an additional wireless access point.  All the small business options I have found seem to be rated as unstable.  Oh, and I do want to keep everything at gigabit speeds.  Thanks!